Blind rivets are fasteners that are permanently installed in a workpiece 26 (see FIG. 2). Most often, the workpiece 26 is formed of two components or layers, but can be in the form of one to multiple components. When there are multiple components to the workpiece 26, the components are joined together by the blind rivet fastener. Blind rivets are installed from only one side of a workpiece 26, thus being blind to an opposite side. The portion of the rivet on the blind side of the workpiece is mechanically deformed during installation by compression and expansion to form an upset head. Because blind rivets are installed from only one side of the workpiece 26, they are cost-efficient and versatile.
Blind rivets were originally designed to accommodate situations where only one side of the workpiece was accessible to the installer. Early adopters of the blind rivet include the automobile industry and the aircraft industry. Blind rivets offer numerous benefits to installers, including speed of installation, versatility, simplicity, and relatively low installed cost in most instances. Unlike many other fasteners, it is generally not possible to under-torque, over-torque, or loosely set a blind rivet since the clamping load is determined by a predetermined breaking load of the blind rivet mandrel.
A blind rivet 10 is conventionally a two-piece fastener that consists of a hollow rivet shank or body 12 having a flared flange 14 portion at one end, and a mandrel 16 passing through the blind rivet body 12 (see FIG. 1). The flange 14 end is the head of the blind rivet. At the opposite end of the body 12 is either an aperture 18, or a closed end (not shown), either of which couple with a head 20 portion of the headed mandrel 16. A one-piece (or closed end) version has a body that is fixedly and integrally coupled with the mandrel, while the two-piece version has a body that is removably coupled with the headed mandrel. The two-piece version is formed by inserting a mandrel with a small interference fit bulge into the blind rivet body.
The rivet body 12 is typically round. The diameter of the rivet body 12 and the grip length that the blind rivet is capable of fastening determines the blind rivet size. A hole, or core 22, most often extends along the length of the rivet body 12.
The mandrel 16, while coupled with the rivet body 12 at one end, extends or protrudes beyond the flared flange 14 portion of the rivet body 12 at the opposite end, creating an exposed portion 30 of the mandrel 16 having a length dimension PPA. Most often, the mandrel 16 closely resembles a nail or wire structure.
A riveting tool physically grabs the exposed mandrel portion 30 that extends beyond the flange 14 portion of the rivet body during installation of the blind rivet. During installation, the rivet body 12 is inserted in a hole in the workpiece 26. After passing through a blind riveting tool anvil, jaws grip the portion of the mandrel that extends beyond the flange 14 of the rivet body, i.e., the exposed mandrel portion 30, and pull the mandrel 16. Because the flange 14 of the rivet body 12 holds the rivet body 12 in place, and the mandrel head 20 is larger than the aperture 18 of the rivet body 12 at the opposite end of the blind rivet 10, the rivet body 12 compresses longitudinally and expands radially outwardly to form a blind-side head. At a predetermined setting force or tensile load, the mandrel 16 is generally designed to break away at or proximal to the head of the mandrel (or the approximate location at which the mandrel couples with the rivet body). Thus, a significant portion of the mandrel 16 falls out of the rivet body 12 in the setting process. The portion that breaks away is sometimes referred to as a spent mandrel 24. A blind head 28 is on the blind side of the workpiece 26 after the rivet has been set, and the rivet flange 14 is on the work side of the workpiece 26, thus holding the workpiece 26 together.
Blind rivets are available in a variety of, diameters, materials, and head styles. Materials used to form the blind rivets include steel, stainless steel, aluminum, copper, brass, and plastic. Blind rivets are commonly classified as either pull-type or drive-pin-type fasteners.
However, generally there is no significant variation in the length dimension PPA of the exposed mandrel portion 30. In fact, the length dimension PPA of the exposed mandrel portion 30 has been standardized. One of the standards organizations that specify requirements of blind rivets in the United States is the Industrial Fasteners Institute of Cleveland, Ohio. Under the IFI STANDARD®, and specifically IFI-114, the length of the exposed mandrel portion is identified as “P” in Table 1 of the Standard. In all instances, dimension “P” is specified to have a dimension of 1-inch or greater (IFI-114—Standard for Break Mandrel Blind Rivets—Issued: November 1973; Revised: February 2003).
The 1-inch minimum dimension of the IFI-114 Standard (dimension “P”) indicates that the portion of the mandrel extending beyond the flange 14 portion of the rivet body, i.e., the length dimension PPA of the exposed mandrel portion 30, must be at least 1-inch or more (specifically, 1.0 in. for blind rivets sized #3 and #4 having body diameters of 3/32 in. and 4/32 in. respectively, 1.06 in. for blind rivets sized #5 and #6 having body diameters of 5/32 in. and 6/32 in. respectively, or 1.25 in. for blind rivets sized #8 having a body diameter of 8/32 in., according to the Standard). This means that the mandrel 16 itself will typically have a length of about one inch plus the distance of a length dimension LRB of the rivet body 12 to the mandrel head 20. Because the mandrel 16 most often breaks at or proximal to the mandrel head 20, in almost all instances of blind rivet installation, the spent mandrel 24 (the portion that breaks away during the setting operation) has a length dimension LPA of at least 1-inch, and is most often greater than 1-inch or more by the length of the rivet body.
The spent mandrel 24 is often discarded by the installer, i.e., thrown away, after each blind rivet is set. In instances where companies have a high volume of usage for rivets, the quantity of spent mandrels can be very significant, on the order of hundreds to thousands of pounds per year. There are costs associated with the mandrels both at the manufacturing end where the rivets are made, and at the user end where the rivets are installed and the spent mandrels need to be disposed of in some form or another. Specifically, at the manufacturing end, there are raw material (steel, stainless steel, aluminum, brass, copper, plastic, etc.) costs relating to the amount of material required to form the rivet and mandrel. At the user end, there are costs associated with collecting, storing, and disposing of the spent mandrels, especially at locations where there are large quantities of rivet usage.
Any reduction in the length of the mandrel, below the 1-inch plus IFI-114 Standard dimension for the length dimension PPA of the exposed mandrel 30, would result in a decrease in costs both at the manufacturing end (reduction of material costs) and at the user end (reduction of costs related to collection, storage, and disposal).
However, because the IFI and others have standardized the exposed mandrel portion 30 length dimension PPA, there has been no recognition of this problem. The standardization helps to avoid the necessity of having dramatically different riveting tools required for different mandrels. A predictable dimension of 1-inch plus means that those developing and manufacturing riveting tools can design those tools to receive a 1-inch plus exposed mandrel portion length dimension. Additionally, to develop a sufficient grip on the mandrel to pull the mandrel to deform the rivet body and then farther to the point of mandrel breakaway, the metals used to form the mandrels required a 1-inch plus exposed mandrel portion length dimension. This 1-inch plus dimension ensures that there is enough surface area on the mandrel to be inserted into the riveting tool and to be sufficiently gripped. If there is too little surface area that can be gripped by the riveting tool, then problems can develop in setting the rivet, such as the jaws of the riveting tool slipping off the mandrel at the higher tensile loads required for break away. However, this 1-inch plus dimension is merely a historical practice.
For at least the issues of the standardization of the length dimension PPA of the exposed mandrel portion (the 1-inch plus minimum dimension) and the requirement of having sufficient surface area of the mandrel to be griped sufficiently, the length dimension PPA of the exposed mandrel portion has not been adequately addressed or designated by the present standards and conventions in a way that also maximizes efficiency of material use and minimizes costs for production, use, and spent mandrel disposal.